1. Field of the Invention
The present invention relates to the field of plasma processing and, more particularly, to the use of plasma equipment for modification of materials.
2. Prior Art
Plasma processing equipment is used extensively in the industry for the modification of materials. These modifications include etching and deposition of films for fabrication of microelectronic circuits in semiconductor devices. The modification may also include implantation of chemical species that change the friction and wear properties of surfaces.
Plasmas generated by high-frequency electrical discharges have important technological applications, including the processing of materials for the fabrication of microelectronic circuits. As technology advances due to competition, industry requires and benefits from improving control over the properties of these plasmas.
A plasma is a gas (or a gas mixture) which is energized so that it is partially decomposed into species that are electrically charged. A variety of techniques are known for energizing the gas. One commonly used technique is the energizing of the gas by imposing on the gas an electric field from an external source. A common practice is to use high frequency alternating current (AC) fields to energize or excite the gas. Techniques for utilizing radio frequency (RF), as well as microwave fields of higher frequencies are well-known in the art. In some instances, these electric fields are utilized in combination with magnetic fields which are used for the purpose of confining the plasma. Electron cyclotron resonance (ECR) plasma processing is one technique for controlling the plasma with the use of electric and magnetic fields.
Plasmas are normally contained in chambers called reactors that separate the plasma from the surrounding work environment. Electrical energy sources and raw-material sources are coupled to the reactors through a variety of interfaces and control circuits. The resulting plasmas are characterized by many properties. Typically, the plasmas contain electrons along with a neutral and charged atoms and molecules of a variety of gas-phase species, all of which have unique, spatially dependent velocity distribution functions. The plasma properties determine the performance of industrial plasma processes.
To achieve certain desired plasma properties, an operator of a plasma-processing system can adjust several controls, each of which is indirectly related to the plasma properties. These controls typically include gas-flow rates, total pressure, and electrical excitation level. The controls also can be modulated and timed during a particular process. It is generally appreciated in the industry that (1) plasma properties are related to such controls in complex ways; that (2) there are a greater number of properties of importance than there are independent controls; and that (3) there is much need for improvement in the ability to control plasma properties. One area for improvement is in developing additional controls so that an operator can have greater capability of achieving desirable set of plasma conditions. The present invention provides for one of these improvements in controlling a set of plasma conditions.